Tooling Article

Trio of New Presses Gets SMED Upgrades

A Stemco press operator and setup technician change out a compound die on one of the firm’s three new mechanical presses. Adding hydraulic die lifters, clamps and electronically valved controllers to each of these presses sliced die-change time nearly in half; the firm calculated an 18-month return on investment for the quick-die-change apparatus.

When Stemco (Specialized Truck Equipment Manufacturing Company) process engineer Andrew Rucker began to explain to me why the firm recently invested in quick-die-change (QDC) equipment on its three new mechanical presses, he glossed over typical criteria such as a quick return on investment and improved productivity —both of which, by the , have seen impressive results due to the move to QDC. Instead, Rucker says that adding hydraulic die lifters, clamps and electronically valved controllers “shows our operators that we want to help them do their jobs better. Performing as many as six setups per shift on each press, the guys on the floor now work more quickly and safely than ever, and operator job satisfaction is at an all-time high.”

Stemco, Longview, TX, primarily supplies aftermarket parts for the wheel ends of tractor-trailers, producing 13 to 15 million metal-stamped parts per year. Most stampings are assembled into wheel seals; each seal takes two to five stampings and measure 4- to 7-in. outside dia., and are of draw-quality steel from 12 to 20 gauge thick.

The firm’s pressroom houses 13 mechanical presses from 40 to 250 ton capacity. “We schedule our manufacturing load one day at a time using a kanban approach,” says Rucker. “The goal is to produce and ship in 48 hr.; we use what we produce, keeping only a few day’s worth of inventory on the shop floor.”

QDC: A Process

The Stemco pressroom embarked on a QDC mission in 2004 by implementing die-change process improvements such as prestaging of dies in die racks located nearby its presses, and by investing in die carts to efficiently move dies around the plant. “Also during that time,” adds Rucker, “we had been on a press-rebuild schedule of one press per about every five years, and finally determined that the cost to rebuild an aging press was approaching that to purchase a new press.”

In 2005, rather than rebuild another press, Stemco purchased a new machine —a Model SN1-176 (176 ton capacity, 49- by 30-in. bolster) from Seyi Presses, Inc., Walnut, CA. Along with the new press came hydraulic die clamps and die lifters supplied by PFA, Inc., Germantown, WI. PFA supplies standard QDC products that can easily be customized to accommodate any clamping height by adding nose pieces and base plates to the clamps. The die lifters provided were made specifically to fit the press’ T-slots, measure 30 in. long, boast cam-type rollers and, as a pair, can support 10,000 lb.

PFA supplies standard QDC products that can easily be customized to accommodate any clamping height by adding nose pieces and base plates to the clamps.

Clamps and die lifters are controlled by a hydraulic control unit outfitted—per Stemco’s specification—with electronic valves to allow Stemco to tie the hydraulic controller to the press control, a Wintriss SmartPac 2.

The QDC-system control directs four separate zones—two plumbed for the clamps on the press ram, one zone for the clamps on the bolster and a fourth zone for the die lifters. Also, a pressure switch tied to the press will shut the press down in the event of a pressure loss. The control, via an air-over-hydraulic pump, converts shop air pressure to the required 5000 PSI and ensures consistent clamp force. Operator safety is enhanced since the clamps cannot be released while the press operates in the automatic mode.

Die Changes Fast and Easy

“The PFA setup immediately took our die-change times from 15 min. down to 8 min.,” says Rucker. “And, because of the the clamps are designed, we can set them up and slide them out of the easily, moving the dies in and out without worrying about damaging the clamps. Die changes are simple enough now that our press operators often take over at the end of a die change, freeing up our die setters to spend more time moving about the shop and focusing on the next setup.”

Integrating its new QDC-outfitted Seyi press into its overall pressroom production flow went so smoothly that Stemco decided to add two more similarly outfitted 176-ton Seyi presses to its stable—one each in 2005 and 2006. Now the three new QDC-equipped presses handle all of the firm’s higher-volume stampings, each press responsible for eight to 10 of Stemco’s hardest-working dies, some of which might stay in the press for just a few hundred hits and others that might run as many as 2000 parts per run. Stroke rate averages 30 hits/min.

“Our return-on-investment calculation for the QDC apparatus showed a payback period of just 18 months for each press,” says Rucker. “And, again, it’s been the best thing we could have done to support our people working on the shop floor.

“Our pressroom had been abandoned for a long time,” Rucker adds, referring back to the beginning of the decade. “At one time we considered outsourcing our stamping work overseas, but ultimately decided that to ensure we receive the part quality we need and the part-order flexibility required to satisfy our lean initiatives, we had to invest in the stamping technology to get it done here. So far so good.” MF